Phosphofructokinase is the key regulatory enzyme of glycolysis in all mammalian tissues. Therefore it is important to understand the structure and function of the isolated enzymes of a variety of tissues. We are currently investigating phosphofructokinases from rabbit muscle and the structure will be investigated. The results thus far indicate that the enzyme consists of two unidentical subunits, and the one of the subunits has been identified as muscle type subunit. The other subunit has not been clearly identified. The subunit composition, N-terminal amino acids and various polymeric states of the enzyme will be investigated. The kinetic and allosteric properties including possible inhibition by ATP, 2, 3 DPG, hexose-P2 and citrate as well as their binding constants will be determined. The binding of fructose-P2 and glucose P2 by muscle and erythrocyte phosphofructokinase will be studied, since it appears that these compounds are the most potent activators of the enzyme. The possible competition with the other effectors is also investigated. Phosphofructokinase and fructose-bis phosphatase are involved in a futile cycle of carbohydrate metabolism. The levels of these enzymes have been suggested to change under various nutritional conditions and hormonal controls. We will investigate possible changes in their activity in rats and the protein concentrations under variety of conditions including a short term change induced by insulin or glucagon administration. BIBLIOGRAPHIC REFERENCES: Uyeda, K., and Kurooka, S. Phosphofructokinase from Clostridium pasteurianum, in Methods in Enzymology (1975) XLII, pp. 86-91, ed. W.A. Woods, Academic Press, New York. Ramadoss, C.S., Uyeda, K., and Johnston, J.M. (1976) Studies on Fatty Acid Inactivation of Phosphofructokinase, J. Biol. Chem. 251, 98-107.